(1) Field of the Invention
The present invention relates to an electronic fuel injection control system for an internal combustion engine, and more specifically to an electronic fuel injection control system using a single control unit that controls the quantity of injected fuel for an internal combustion engine having a plurality of cylinders arranged in two banks and having two corresponding exhaust manifolds of the type such as in a V-8 engine.
(2) Description of the Prior Art
With rapid developments in electronic technology in recent years, electronic engine control systems using microcomputers have been developed for carrying out fuel injection control, spark timing control, EGR (Exhaust Gas Recirculation) control, idling speed control, and so forth in a unified fashion.
For example, in the case of a fuel injection control system for an in-line six-cylinder engine, for each revolution of the engine, before the fuel injectors are actuated to inject fuel, a microcomputer of a control unit performs an arithmetic operation to calculate a basic fuel injection pulse width (a basic amount of injected fuel per engine speed) T.sub.p which is proportional to an intake air flow quantity with respect to engine speed (T.sub.p =Q/N x Constant, where Q represents the intake air flow quantity and N represents the engine speed).
Next, a feedback signal from an exhaust gas sensor, (e.g., an oxygen sensor which senses and signals the concentration of oxygen in the exhaust gas from the engine to obtain an air-fuel mixture ratio of the fuel supplied to the engine) is inputted to the microcomputer where a correction coefficient .alpha. is calculated to correct the air-fuel mixture ratio to a stoichiometric air-fuel mixture ratio. The basic fuel injection pulse width T.sub.p is multiplied by other correction coefficients COEF and the calculated result .alpha. to calculate the fuel injection time T.sub.i. The calculated value T.sub.i is then set into the injection time register.
The start of injection for the in-line six cylinder engine of the present example is adapted to synchronize with a 360.degree. signal produced by a pulse signal from a crank angle sensor comprising for example three magnetic heads and a waveform shaper for outputting a pulse each time the crankshaft rotates, in the above example, through 120.degree.. Using the pulse signals, a 360.degree. signal representing a single engine rotation is produced by means of a divider. Simultaneously, a counter starts counting the pulses generated during a fixed time interval and a microcomputer compares the counted value with the value in an injection time register of the control unit and stops the injection when the two values coincide.
Consequently, one fuel injection per revolution of the engine can be performed having the proper fuel injection time duration depending on the period of time set in the injection time register. The fuel injection pulse signal, whose width corresponds to the fuel injection time, is respectively fed to a power transistor connected to a solenoid associated with a fuel injector. As the transistors are turned on and off, current flows through each solenoid in turn and the associated fuel injector valve is opened to distribute a fine spray of fuel into the corresponding engine combustion chamber.
When a similar system is applied to a V-8 engine, whose cylinders are arranged in two opposing banks of four cylinders, the intake and exhaust manifold systems are branched into two systems corresponding to the two cylinder banks respectively so that the oxygen sensors are also positioned in each of the two exhaust manifolds. These dual systems will hereinafter be referred to as right and left systems, e.g., right cylinder banks, left cylinder banks, etc.
Since the correction value for the air-fuel mixture ratio against a stoichiometric air-fuel mixture ratio may be different for each of the banks, that is, the required amount of fuel injection per revolution may vary between the right and left cylinder banks, the fuel injection time T.sub.i must be determined separately for the right cylinder banks and for the left cylinder banks. For this reason, separate control units, such as those used for the in-line cylinder type of engine, are provided for each of the two engine fuel injection control systems. Therefore the cost of these control units is doubled and mass production of the fuel injection control system may become uneconomical.